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Preventive effect of soybean resistant proteins against experimental tumorigenesis in rat colon
1Department of Biological Resource Chemistry, Kyoto Prefectural University, Japan.
Abstract:
The insoluble 'high-molecular-weight' fraction (HMF) centrifugally separable after digestion of soy protein isolate with a microbial protease of the exo-type, of which about a quarter is regarded as an indigestible 'resistant protein,' was examined for its preventive effect against colonic tumorigenesis in a model system with male F-344 rats. The rats were intraperitoneally injected with azoxymethane (15 mg/kg BW) once a week for 3 wk and were fed a 20.6% HMF diet (+0.4% DL-Met) or 14.7% casein diet (+0.3% DL-Met) supplemented with 0.2% sodium deoxycholate (DCA) or without supplementation. Twelve wk later, 5 rats of each group were inspected for formation of tumors but no tumors were visible to the naked eye. The DCA-fed casein group was conspicuous for a low count of aberrant crypt foci. At 39 wk, 6 rats of the DCA-fed casein group (n = 10) and 3 rats of the DCA-fed HMF group (n = 9) had a total of 18 tumors with a major axis of 4.0 +/- 0.4 mm and 3 tumors with an axis of 2.0 +/- 0.1 mm, respectively, in contrast to only a single tumor for the DCA-unfed casein group (nil for the DCA-unfed HMF group). The difference in tumor number and size was considered significant between these DCA-fed casein and HMF groups; that is to say, HMF feeding retarded tumor development despite the frequent occurrence of pre-neoplastic lesions. In addition, fecal bile acid excretion was much more elevated by HMF feeding than by casein feeding. It can be assumed from these observations that the antitumorigenicity of HMF is due to the inhibitory effect of soybean resistant proteins on reabsorption as well as the mucosal contact of bile acids in the intestine.
Insights
High-molecular-weight fraction (HMF) from soy protein isolate showed preventive effects against colon cancer in rats. HMF feeding reduced tumor development and size, suggesting potential benefits of resistant soy proteins.
Area of Science:
- Gastroenterology
- Oncology
- Nutritional Science
Background:
- Colonic tumorigenesis is a significant health concern.
- Dietary factors play a crucial role in cancer development.
- Soy protein isolate contains indigestible resistant proteins with potential health benefits.
Purpose of the Study:
- To investigate the preventive effect of high-molecular-weight fraction (HMF) from soy protein isolate against colonic tumorigenesis.
- To evaluate the impact of HMF on tumor development in a rat model.
- To explore the role of bile acid metabolism in HMF's potential anti-tumorigenic effects.
Main Methods:
- Male F-344 rats were injected with azoxymethane to induce tumors.
- Rats were fed diets containing HMF or casein, with or without sodium deoxycholate (DCA).
- Tumor formation, aberrant crypt foci, and fecal bile acid excretion were monitored over 39 weeks.
Main Results:
- HMF feeding significantly retarded tumor development and reduced tumor size compared to casein feeding in DCA-supplemented groups.
- DCA supplementation led to fewer aberrant crypt foci in the casein group.
- Fecal bile acid excretion was significantly higher in rats fed HMF compared to casein.
Conclusions:
- High-molecular-weight fraction (HMF) from soy protein isolate exhibits anti-tumorigenic properties against colonic tumorigenesis in rats.
- The anti-tumorigenic effect is likely mediated by soybean resistant proteins inhibiting bile acid reabsorption and mucosal contact.
- HMF represents a promising dietary component for colon cancer prevention.